Dynamic random access memory (DRAM) components, such as those illustrated in FIG. 1A, provide an inexpensive solid-state storage technology for today's computer systems. Digital information is maintained in the form of a charge stored on a two-dimensional array of capacitors. One such capacitor is illustrated in FIG. 1B.
FIG. 2 illustrates a prior art memory system including DRAM with the corresponding control, address and data wires which connect the DRAM to the processor or memory controller component. In synchronous DRAMs, a write access is initiated by transmitting a row address on the address wires and by transmitting row address strobe (RAS) signal. This causes the desired row to be sensed and loaded by the column amplifiers. The column address is transmitted on the address wires and the column address strobe (CAS) signal is transmitted along with the first word of the write data WData(a,1). The data word is then received by the DRAM and written into the column amplifiers at the specified column address. This step can be repeated “n” times in the currently loaded row before a new row is sensed and loaded. Before a new row is sensed, the old row must be restored back to the memory core and the bit lines of the DRAM precharged.
FIG. 3A illustrates synchronous write timing. In the figure, a, b . . . represent a row address; 1, 2 . . . n represent a column address, WData [row, col] represents the DRAM address of data words, the row address strobe (RAS) is a control signal for initiating a sense operation, and WRITE(CAS) initiates the write operation on the column amplifiers. In the present example, the row column address delay timing parameter is equal to two clock cycles. After the row address is asserted at the first clock cycle, column addresses and write data are asserted after the delay to write the data into the DRAM array.
FIG. 3B illustrates synchronous read timing. A processor initiates a read access by transmitting a row address on the address wires and by transmitting the row address strobe (RAS) signal. This causes the desired row to be sensed by the column amplifiers. The column address is then transmitted on the address wire and the column address strobe (CAS) signal is transmitted. The first word of the read data RData (a,1) is then transmitted by the DRAM and received by the processor. This step can be repeated “n” times in the currently loaded row before a new row is sensed and loaded. Before a new row is sensed, the old row must be restored back to the memory array.
Various attempts have been made to improve the performance of conventional DRAMs. Such attempts have resulted in DRAM architectures that deviate in varying degrees from conventional DRAM architectures. Various alternative DRAM architectures are described in detail in NEW DRAM TECHNOLOGIES, by Steven A. Przybylskti, published by MicroDesign Resources, Sebastopol, Calif. (1994). Some of those architectures are generally described below.